<div id="left">
  
  <div id="widget_category" class="widget widget_categories">
    <h3>category</h3>
    <?php display_category_tree();?>
  </div>

  <div id="widget_page" class="widget widget_page">
    <h3>page</h3>
    <?php display_page_tree();?>
  </div>

</div>